Since our discovery of Arich element (ARE)-binding protein/degradation factor AUF1 in 1991, this protein family has been increasingly linked to many biological processes. These processes include cellular proliferation, inflammatory responses, transcription of cellular and viral genes, and maintenance of both telomeres and epigenetic integrity of the cell. Work from many laboratories, including the recent report of auf1-/- mice, has firmly established its participation in ARE-mediated mRNA degradation (AMD). During the prior funding period, we examined mechanisms of AUF1 action in AMD. Our key findings were that AUF1 acts within the context of a multi-protein complex that includes translation initiation factors and dual-functioning ARE-binding/heat shock proteins, and that AUF1 possesses an RNA chaperone-like activity that might control assembly of this protein complex. AUF1 thereby links the ARE-mRNP to the mRNA degradation machinery. We unexpectedly discovered that AUF1 controls translation in an ARE-dependent fashion, independently of its mRNA degradation function. Moreover, participation of AUF1 in translation versus mRNA degradation may be dictated by the specific ARE to which it is bound. Using MYC mRNA as a model, we found that AUF1 and other ARE-binding proteins work in opposition to set MYC translation rates. We also obtained evidence from mutagenesis studies that secondary structure within the MYC 3'UTR contributes to its translational control. As well, microRNA let-7g controls MYC expression and its annealing site is embedded within predicted regions of RNA secondary structure. Based upon these observations, our central hypothesis is that specific RNA-binding proteins and microRNAs, as well as 3'UTR secondary structure, conspire to set translation levels of MYC and other ARE-mRNA subsets. A corollary hypothesis is AREs may contain embedded regulatory codes dictating translation versus degradation (or both). We plan to utilize human cell culture systems and a combination of genetic and biochemical approaches to examine our hypotheses. Specifically, we will: (i) examine mechanisms of AUF1- directed translational activation;(ii) examine contributions of AUF1 to RNA structure, availability of the let-7g target site, and translation, and (iii) examine differential, AUF1-dependent association of trans-acting factors with degraded versus translationally-regulated ARE-mRNAs. PUBLIC HEALTH RELEVANCE The public health significance of these studies is highlighted by the fact that proper regulatory control of many ARE-mRNAs is essential, as their deregulation is central to formation of many tumors. Proper control of certain genes is important for normal cell division and development. When control of these critical genes is lost, cancer often results. We discovered a protein called AUF1, which is responsible for control of genes involved in cell division. We are studying the mechanisms by which AUF1 controls these genes, which will help us to understand processes by which normal cells can become cancer cells.